As is known in the art, tanks containing fluids under pressure are often provided with pressure relief valves. Such tanks may exist, for example, on railroad tank cars. Pressure relief valves typically use a compression spring to maintain the valve in a closed condition. When the pressure in the tank exceeds a pre-determined level, the spring force holding the valve in the closed condition is overcome and the valve opens so that fluid from the tank is vented to ambient so as to lower the pressure within the tank. An example of such a pressure relief valve is presented in U.S. Pat. No. 3,131,718 to Mingrone.
Pressure relief valves that are spring powered typically have a stem axially aligned with the motion of the valve closure member. This stem typically passes through the center of a coil spring and is typically used to set the compression spring at a correct height (or extension if a tension spring is used to achieve the force for the desired pre-determined venting pressure. In the event that the spring is not compressed before removing the component used to set the spring, such as during disassembly of the valve for service, repair or replacement, the spring can release stored energy in unpredictable directions. In the theoretical scenario of stein breakage or other component failure, the spring force can also be released in the unpredictable directions.
A need therefore exists for a device that reduces or eliminates the risk of accidental release of spring forces in a pressure relief valve assembly.